With advances of sciences, technologies and industries, it is desirable for video and audio devices to simulate real scenes. Head-mounted 3D displays, as emerging technologies in recent years, can bring vivid images to users for existing two-dimensional images so that the users can feel that they are personally on the scene. The display principle lies in that left and right eye images are respectively displayed on a display screen to form a slightly different image at the retina of each of the user's two eyes, which causes the visual centers of the brain to combine the two images into a single complete image with a 3D effect. The inventor of the present invention finds that, as different users have different interpupillary distances, deviations in the application effect of head-mounted 3D displays will appear. Therefore, head-mounted 3D displays should have an interpupillary distance adjustment function to be adapted to different users.